This reverts commit a38e42f6.

This reverts commit fad5c8e3.

This reverts commit 0e28a39d.

This reverts commit f525cea0.

This reverts commit 6e77bd6c.

This reverts commit 0d7e595f.

This reverts commit 73e2cde6.

This reverts commit 5a6fe171.

This reverts commit d3941dc1.

This reverts commit 32593b63.

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This reverts commit 428edb6f.

This reverts commit 9e683d0d.

1. ModelSaver();
2. _build_ema_model();
3. _init_checkpoints();
4. others.

1. rm engine.device and use paddle.device.get_device() instead;
2. mv some code to build_train_func or build_eval_func to simpfy engine.